There is a consensus among psychologists, neuroscientists, and clinicians that the consumption of addictive substances leads to malfunctions of brain's decision-making circutry, which eventually lead to systematic pathological choice. Advancements in behavioral neuroscience and neuroeconomics over the last decade have lead to the development of a number of competing theories about the nature of the underlying dysregulatory processes. One of the most prominent theories states that addiction is the result of a dysregulation of the reward learning circuitry. This application proposes three experiments that provide the first valid test of this theory. Aim 1 uses computational fMRI approaches imported from neuroeconomics in three novel experimental paradigms to test the theory. The grant also has a training component, Aim 2, designed to improve the nation's biomedical research base by training the Principal Investigator, a PhD student, and a post-doc on how to apply their knowledge on the neurobiology of decision making to the study of addiction. PUBLIC HEALTH RELEVANCE: A necessary condition for developing more successful treatments and prevention programs for addiction is to understand what are the mechanisms through which the addictive substances interfere with the proper functioning of the brain's decision-making circuitry. Advances in behavioral neuroscience over the last decade have lead to the development of a number of competing theories about the nature of the underlying dysregulatory processes. One of the most prominent competing theories states that addiction is the result of a dysregulation of the reward learning circuitry, and in particular of the computations that are encoded by the mesolimbic dopamine system. The neuroimaging experiments proposed in this application will provide critical new tests of this theory. Testing this theory is important because both its validation and its refutation will advance public health by narrowing down the set of possible mechanisms that clinicians and neuropharmacologists will have to consider in developing new treatments for addiction.